I know its hard but weight gain is not the only sign that bub is getting enough and doing ok. What are her nappies like? What is her skin like?
It's great that you are getting some good breastfeeds happening now. If you can hang in it will get easier, babies know where the good stuff is if you give them the option.
I hope the weigh in goes well, but try not to have everything dependent on what happens tomorrow. Bub being sick can affect weight gain, because they are using energy to fight the bugs, and maybe not so much into growing.
I remember giving bub an extra feed in the waiting room, and hoping she wouldn't poo before the weigh in so it would give her extra weight . Sometimes i would feel disheartened cos she only had a small gain but the next week she would have a big one, i learnt (it took awhile) to try not try stress cos bub was ok, and that was just her weigh gain pattern.